Exact biexciton binding energy in carbon nanotubes using a quantum Monte Carlo approach

We performed quantum Monte Carlo (QMC) calculations for a model system of excitons and biexcitons in carbon nanotubes (CNTs) and compared the results with those of a variational approach [T.G. Pedersen, K. Pedersen, H.D. Cornean, P. Duclos, Nano Lett. 5 (2005) 291]. Due to their geometric properties, the shape of a hollow cylinder, CNTs can be treated as 2D objects. With decreasing diameter one expects them even to exhibit quasi-1D properties. In the present study the biexciton in its ground state is found to be more strongly bound than estimated before. Biexcitonic complexes are predicted to remain stable for all diameters even at room temperature. The binding energy grows significantly with decreasing diameter, showing indeed a transition from a quasi-2D system to a quasi-1D system.